"Class A" compressors?

[BertKoor]

Hi everybody!

I have been "lurking" here for some months. Boy, this site is full of knowledge! Now I have a question that Google has not answered for me.

What exactly is a "Class A" compressor? I read it in some advertisements. Is it a special design, or just comforting words so I will trust them?

I googled for "class B compressor" also, but they seem to be fitted only in refrigerators

Thanks in advance! I know you guys can be fast....

[jones-y]

Class A refers to the quality of the components used in building the device. Its called class A for a reason. This refers to solid state devices (devices built with transistors, instead of tubes)

[jones-y]

Here's what Google turned up:

Class A – A relatively inefficient amplifier design in which the output devices conduct current all the time. Pure class A devices generate large amounts of waste heat, but are usually thought to have good sound quality.

[BertKoor]

Thats a fast response, guys! I did not find that description in Google.

What would you call "good sound quality" amplifier? Will it be significantly better than e.g. a Behringer? Or does Behringer also use class A stuff?

Thanks anyways!! KVR is great, I'm getting the hang of it now...

[jones-y]

Class A is a design concept, which is supposed to be coupled with quality components.

I'll let you sort out the rest WRT Behringer...

As far as its use, it does see a fair amount of marketing abuse.

[BertKoor]

Ah, so it is a bit of both... Comforting design.

Sorry for my ignorance, I did not understand this small part: WRT = Wurlitzer Rhodes Tribute?

[jones-y]

"With respect to"

same as saying: "as it pertains to" or "in the case of"

[bk]

Class A refers to the quality of the components used in building the device. Its called class A for a reason. This refers to solid state devices (devices built with transistors, instead of tubes)

This is incorrect. Class A refers to the fact that the devices (be they tube or transistor) are turned on through both positive and negative swings of the signal. Class AB on the other hand, uses one device for the positive side and another device for the negative side.
The detrimental effects (on the signal) of switching these devices on/off is what Class A eliminates. That's it's claim to fame.
The disadvantage of class A is efficiency and in the end, power output. Class A amps are typically a lot lower output than their AB counterparts.
Most plain vanilla power amps are some variant of class AB.

[Notron User]

Class A power amplifiers can generate a lot of heat. But its not so bad with preamplifiers.

I have a buzz ma 2.2 preamp, and it doesn't require fans. I think they even advise leaving it on all the time.

Amplifiers are another matter.

I have an old integrated amp that is biased towards class a operation. For the first 8 watts of power it operates in class a, the rest it slides into ab.

It draws 70watts at standstill and feels about as hot as a lightbulb. Its entire top is a heatsink.

[ew]

Class A refers to the quality of the components used in building the device. Its called class A for a reason. This refers to solid state devices (devices built with transistors, instead of tubes)

This is incorrect. Class A refers to the fact that the devices (be they tube or transistor) are turned on through both positive and negative swings of the signal. Class AB on the other hand, uses one device for the positive side and another device for the negative side.
The detrimental effects (on the signal) of switching these devices on/off is what Class A eliminates. That's it's claim to fame.
The disadvantage of class A is efficiency and in the end, power output. Class A amps are typically a lot lower output than their AB counterparts.
Most plain vanilla power amps are some variant of class AB.

Correct- and that's why a lot of people swear by class A amps as far as recording goes. You can run the amp at close to (if not) full volume, and you won't have any of the high volume troubles such as bleedthrough, but you'll still have that cranked amp sound. Great in clubs as well- I used a Boogie Mark III in class A mode as my gigging amp for years
ew

[McLilith]

Of course, those comments about heat generation are correct for Class A amplifiers, but there will be little heat generated in a typical preamp, or compressor circuitry. The loss of power efficiency is also not a huge concern, because even though it might be inefficient, the power consumption is still relatively small for a preamp or compressor circuit. (The same applies to tone controls, an EQ, or most other line-level circuitry.) To be fair, the increased power consumption, might become a concern in battery powered gear.

In theory, Class A should generally have a performance advantage, but the end results still depend on the quality of components used, the exact circuit design, etc. Like others have said, it is sometimes used as a marketing ploy, to conceal other, less-desirable aspects of a product. Kind of like taking a basically crappy preamp design and sticking a vacuum tube into it, just to be able to claim the crappy preamp has "vintage tube warmth" or something like that.


take care,
McLilith

[bk]

The disadvantage of class A is efficiency and in the end, power output. Class A amps are typically a lot lower output than their AB counterparts.

Sorry for derailing the thread. Somewhere in my rush to set the world straight about class A, I got off on a tangent about power amps.
McLilith is of course completely correct about the disadvantages of classA in line level signal equipment being minimal compared to power amps.

[Tubeman]

Class A refers to the quality of the components used in building the device. Its called class A for a reason. This refers to solid state devices (devices built with transistors, instead of tubes)

Class A has nothing to do with the quality of the components or is it solid state or tube. It only refers to the way how gain stages are designed. Class A is not necessarily better than Class AB.

[antti]

Correct- and that's why a lot of people swear by class A amps as far as recording goes. You can run the amp at close to (if not) full volume, and you won't have any of the high volume troubles such as bleedthrough, but you'll still have that cranked amp sound.

Have you actually tried really cranking up class A guitar amp?
I have built AX84 HiOctave, which is only 5 watts, and it can hold it's own against any drummer. You definitely need earplugs when playing (unless you want to get hearing damage real fast).

A quick calculation gives maximum SPL of 105dB at 1m from the speaker.

As for the original question, class A compressor probably means that all amplifiers in the signal path run at class A. This would be a given with most tube circuits or discrete transistor circuits. Almost all opamps are class AB though.

[BertKoor]

Alright.. I am not so worried for a compressor cirquit to be not 100% efficient with power. How many watts will it consume, maybe one?

So I understand a "class A" compressor does not have normal opamps inside. Would a standard opamp be of the balanced push-pull type then, with one doing the plus phase and another doing the minus phase?